Objectives: In this study, we characterized the frequency tuning of bone-conducted sound-evoked myogenic potentials recorded from extraocular muscles (BOVEMP) in normal human subjects.
Study design: Experimental design.
Methods: In a sample of nine subjects, acoustic tone bursts (57 dB nHL, 8 ms plateau, 1 ms rise/fall, alternating polarity) with frequencies from 250 Hz to 2,000 Hz were delivered by a bone oscillator (Radioear B-71) placed on the left mastoid processes. Subjects were required to sit upright and maintain a straight gaze. The BOVEMPs were recorded from surface electrodes placed at four locations around the right eye (superior, inferior, nasal, and temporal) and referenced to an electrode placed at the nape of the neck over cervical vertebrate C7. Signals from electrodes were amplified (10,000 gain) and sampled at 10 kHz and were averaged over 500 repetitions.
Results: Short latency biphasic potential were present at each of the four recording sites around the eye. The average latency of the first peak (negative) and the second peak (positive) was 15.7 ± 0.3 ms and 23.3 ± 0.5 ms, respectively. The tuning curve of the BOVEMP was similar at each recording site with largest N1 amplitude following stimulation at 383 Hz (± 17 Hz) and largest P1 amplitude following stimulation at 440 Hz (± 22 Hz).
Conclusions: Since the frequency tuning for the bone-conducted sound-evoked OVEMP (BOVEMP) was different from that of the air-conducted sound-evoked OVEMP (AOVEMP), we hypothesize that the BOVEMP and AOVEMP are generated by activation of different vestibular end organs.